A loose grammar for a bluescript file:

General notes:
	-- any char including '\n', but excluding the virtual char 'EOF'
	   is rendered "unspecial" by the '\' escape.  As a consequence,
	   '\\' is required to represent the character '\'.  Anywhere
	   a range of characters that is defined as a negated set,
	   (e.g. "anything except 'x'") can be assumed to accept an
	   escaped character unless explicitly stated otherwise.
	
	-- literals are defined here either between single quotes
	   (e.g. 'xyz' means the actual characters xyz) or as a 
	   range (e.g. [a-f] means 'a' or 'b' or 'c' or 'd' or 'e' or 'f')
	-- negated ranges are also used (e.g. [^a-f] would meaning anything
	   except 'a' 'b' 'c' 'd' 'e' or 'f'
	-- * == repeated 0 or more times
	-- + == repeated 1 or more times
	-- () == grouping operators
	-- | == choice operator
	-- '\n' == the newline character, [^\n] == anything but the newline
	-- EOF == the virtal 'EOF' character
	
script ::= ( comment | blank | command )*

comment ::= space* '#' [^\n]* ('\n' | EOF)

blank ::= space* ('\n' | EOF)

command ::= (space* elem)+ space*

elem ::= constant | string | variable | list | evallist

string ::= '"' [^"]* '"'

var ::= '$' varname | '${' [^}]* '}'

varname ::= [a-zA-Z_][a-zA-Z0-9_]*

list ::= '{' (space* elem)* space* '}'

evallist ::= '[' command ']'

constant ::= [^${["][^<space>]*

space := ' ' | '\t' | '\r' | '\n'